The present invention is directed to an apparatus and method that extracts and exploits information conveyed within spatial phase (e.g., three-dimensional geometry) characteristics of electromagnetic energy (e.g., light), and is particularly directed to an apparatus and method that extracts data via multi-characteristic spatial phase processing as a novel approach to providing information useful for imagery, data communication, and various other technology areas.
Conventional imaging and/or detection systems employ intensity-based techniques to process electromagnetic energy proceeding from a source (e.g., an object). As one example of a conventional system, a spectroscopic system determines spectral (wavelength) composition of objects and scenes. The wavelengths that comprise the collected energy are separated with the use of a dispersive element employing refractive means, such as a prism, or diffractive means, such as a grating. After passing through one of these dispersive elements, the different wavelength components of the wave front propagate in different directions and the intensities of the components are recorded by an array of detector pixels. Such a standard spectrometer is an excellent device for determining the spectral composition of light emanating from a source object, but is unable to provide viable two-dimensional image integrity of the source object. Typically, such a spectrometer is not capable of determining spectral content on a pixel-by-pixel basis, and merely collects the total intensity of electromagnetic energy proceeding from an object.
Fourier transform and Fabry-Perot interferometer systems are capable of performing imaging spectrometry and determining the spectral composition of an object on a pixel-by-pixel basis. However, there are certain limitations imposed by the geometry of these systems. For example, in both types of systems, field of view of is severely restricted.
For the Fourier transform interferometer, the length of the system, combined with the small size of the mirrors, restricts the field of view because optical rays will not propagate through the system for large angles. Therefore, the number of pixels that can be acquired is limited.
For the Fabry-Perot interferometer, a small field of view is the result of two main effects. First, the light coming from the source object undergoes multiple reflections within a mirrored optical cavity before emerging from the system. When the incident light comes from an off-axis point on the object, it enters the cavity at an incident angle other than zero. Consequently, as the light undergoes multiple reflections, it will xe2x80x9cwalkxe2x80x9d along the mirrors and eventually leak out of the cavity. The result of this behavior is that, as the field of view increases, the energy throughput of the system decreases.
The second problem that results in a limitation of the field of view for the Fabry-Perot system has to do with band pass variation with field size. Since the effective mirror separation changes with field angle, so does the filter band pass. To minimize the spectral variation from the center to the edge of the field, the field of view has to be small. However, this will again limit the number of pixels that can be obtained.
Still another problem that can arise with respect to some known systems, such as the Fourier transform interferometer, deals with image registration. Typically, two-dimensional images are acquired as one mirror is scanned. Problems associated with scanning, such as mirror jitter, uneven scanning, or mirror walking, create registration problems between the images in the different spectral bands.
In addition, many known systems employ scanning to acquire the spectral composition of the electromagnetic energy proceeding from a source object. During such scanning, it difficult to obtain the spectral composition in real-time while maintaining a high signal-to-noise ratio. This is not only a problem for the Fourier transform and Fabry-Perot interferometers, but also for electrically scanned systems such as liquid crystal systems and acousto-optic tunable filter based imaging spectrometers, which have the additional problem of relatively low transmission.
Tomographic-based methods are sometimes used for imaging spectrometry tasks. Tomographic methods negate the need for scanning. However, the downside of this technique is that it is computationally intensive, requiring the mathematically determination of a system matrix, which is usually application specific.
Turning attention to data transmission, it is to be appreciated that numerous techniques and methodologies have been employed. In general, data is conveyed via change (e.g., modulation) of a parameter of transmitted EM energy. For example, amplitude modulation (AM), frequency modulation (FM), quadrature amplitude modulation (QAM), phase modulation, pulse width modulation (PWM), amplitude shift keying (ASK), frequency shift keying (FSK), etc. are techniques and methods that are employed. However, each known technique and methodology has an associated limitation on the amount of information that can thereby be conveyed. However, the inventor has recognized that spatial phase characteristics of electromagnetic energy can be utilized to convey information, and convey greater quantities of information than conventional techniques and methodologies.
Returning again to imaging, conventional detection and identification is predominately done with standard video cameras. Standard video cameras are limited in outputting an 8-bit monochrome intensity scale with limited information. Most efforts in the past have been spent on algorithms and faster processing in an attempt to pull enough information out of the standard video to accurately identify targets of interest. Small advances in the ability of the sensor to collect additional information should increase recognition algorithms by orders of magnitude due to the already advanced state of processing and algorithm development.
Typical 3-D systems fall into several categories, all of which are markedly limited. One type of system requires exact and constant distances from subject and multiple cameras coupled with triangulation algorithms to create 3-D stereovision. This approach is limited to one distance and multiple camera locations. Another approach is to use shadows on the subject to calculate the 3-D curvatures. Complex algorithms that require known lighting positions limit shadow analysis. Another method that has been tried unsuccessfully is laser-gated pulses. This technique works reasonably well for large objects such as tanks but no modifications are on the horizon to adapt the technology to small facial features and contours. Additionally, laser illumination is a potential safety hazard to human subjects. The time-gated technique has a time resolution issue for smaller features.
As mentioned above, conventional imaging techniques employ intensity collection techniques. However, it is to be noted that, in distinction, spatial phase is intensity independent. Spatial phase characteristics of electromagnetic energy include characteristics of the plurality of polarizations (e.g., linear and circular) that are present within the electromagnetic energy. Spatial phase characteristics of electromagnetic energy also include characteristics of the shape or form of the waves present within the electromagnetic energy.
Focusing on polarization, several types of utilization are known. As one type of utilization of polarization characteristics, polarimetry identifies, isolates, and/or uses a generalized polarization of electromagnetic energy. In the past, scientists have used polarimetry to filter imagery for specific applications. Polarization filters are used to collect polarization data, and classical polarization theory is used to determine one level of the spatial phase properties. However, overall spatial phase of a propagated electromagnetic wave can have a significant amount of information that is indicative of unique features about the wave history. For example, properties of an electromagnetic wave change as the wave interacts with media and changes as the wave transverses a surface. Also, the electromagnetic wave retains aspects that are indicative of the interactions with the media and the changes from surface interactions.
Therefore, while some of the prior art is capable of performing limited polarimetry and other intensity-based applications, it is not capable, for the reasons discussed, of providing true, multi-dimensional, real-time spatial phase imaging.
The inventor has recognized that a spatial phase system would solve the above-mentioned problems and also go further into the complete analysis of the phase information, which is contained in the electromagnetic energy. By the scientific analysis of all the radiation being transmitted, reflected, emitted and/or absorbed, one can determine its spatial-phase properties. The spatial-phase properties are those characteristics that convey information (e.g., an indication of the media through which a wave has passed) that could allow significant imaging abilities. Along these lines, the inventor has recognized that spatial phase is a technology with tremendous benefit potential. However, the existence of spatial-phase properties has not led to utilization of the spatial-phase properties. In one respect, utilization of spatial-phase properties has not occurred because of the lack of an ability (e.g., no devices, techniques, method, or processes) to utilize the properties.
In accordance with one aspect, the present invention provides a method of deriving increased information from electromagnetic energy. Values of any of several spatial phase characteristics of the electromagnetic energy are determined. The determined spatial phase characteristic values are used in a manner to provide information.
In accordance with another aspect, the present invention provides a method of deriving increased information from electromagnetic energy. One quantitative-existence value related to at least one spatial phase characteristic of the electromagnetic energy is determined for one portion of electromagnetic energy. Another quantitative-existence value related to at least another spatial phase characteristic of the electromagnetic energy is determined for the one portion of electromagnetic energy or the one spatial phase characteristic of the electromagnetic energy for another portion of electromagnetic energy. The one quantitative-existence value is quantified relative to the other quantitative-existence value. The quantification of the one quantitative-existence value relative to the other quantitative-existence value is used as information.